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Abstract:

The present disclosure provides a polymer electrolyte membrane chemically
bonded with an ionic liquid. More particularly, the present disclosure
provides a polymer electrolyte membrane chemically bonded with an ionic
liquid by reacting the ionic liquid with a novel polymer chain terminal.
The polymer electrolyte membrane described herein has a high hydrogen
ionic conductivity, even in a high-temperature and anhydrous environment.
Additionally, the membrane displays electro-chemical and thermal
stability. Moreover, the polymer electrolyte membrane may also be applied
to a high-temperature and dry-out bio fuel cell.

Claims:

1. A compound of Formula 1: ##STR00008## wherein x ranges from about 10
to about 1000, and y ranges from about 10 to about 1000.

2. The compound of claim 1, wherein x ranges from about 10 to about 100,
and y ranges from about 10 to about 100.

3. The compound of claim 1, wherein x ranges from about 10 to about 500,
and y ranges from about 10 to about 500.

4. The compound of claim 1, wherein x ranges from about 100 to about 500,
and y ranges from about 100 to about 500.

5. The compound of claim 1, wherein x ranges from about 100 to about 750,
and y ranges from about 100 to about 750.

6. The compound of claim 1, wherein x ranges from about 500 to about 750,
and y ranges from about 500 to about 750.

7. The compound of claim 1, wherein x ranges from about 500 to about
1000, and y ranges from about 500 to about 1000.

8. The compound of claim 1, wherein x ranges from about 750 to about
1000, and y ranges from about 750 to about 1000.

9. A method of making a polymer electrolyte membrane, comprising:
reacting the compound of claim 1 with an ionic liquid of Formula 2,
##STR00009## wherein R1 and R2 are independently hydrogen and
C1-C30 alkyl group, and X.sup.- is one or more selected from
BF.sub.4.sup.-, PF.sub.6.sup.-, C2F6NO4S.sup.-, Cl.sup.-,
OH.sup.-, Br.sup.- and CF3SO.sub.3.sup.-.

Description:

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims under 35 U.S.C. §119(a) the benefit of
Korean Patent Application No. 10-2012-0080160, filed on Jul. 23, 2012,
the entire contents of which are incorporated herein by reference.

BACKGROUND

[0002] (a) Technical Field

[0003] The present invention relates to a polymer electrolyte membrane
bonded with an ionic liquid by chemical reaction of the ionic liquid with
a novel polymer chain terminal, and a fuel cell using the polymer
electrolyte membrane.

[0004] (b) Background Art

[0005] Hydrogen conductive polymers have been widely studied for use in a
polymer exchange fuel cell (PEFC), which supplies an environmentally
friendly (e.g., eco-friendly) source of energy. One of the main problems
for the development of hydrogen-conductive polymer technology is the
ability to produce a hydrogen-conductive polymer that has long-term
stability and durability. Unfortunately, the stability and durability of
such polymers is negatively impacted by a variety of factors, including:
carbon monoxide pollution occurring in a platinum catalyst, complexity in
heat and water control systems, moisture maintenance in a polymer
electrolyte, and improvement of reaction speed in an electrode.

[0006] The simplest approach to solve the foregoing problems is to improve
the operating temperature of the PEFC. It is well known that carbon
monoxide pollution in an electrode decreases to the ignorable level as
operating temperature increases. However, such an increased operating
temperature is higher than, or equal to, the boiling point of water,
which requires a low humidification condition. Therefore, there is a need
to develop a system in which a new hydrogen conductor having a high
boiling point and non-volatile property is introduced in place of water.

[0007] At present, Nation® (DuPont) is mostly used as a polymer
membrane of a polymer electrolyte fuel cell that operates at temperatures
in the range of 60-80° C. Nation® is a sulfonated
tetrafluoroethylene based fluoropolymer-copolymer, which is a synthetic
polymer with ionic properties (e.g., ionomers). Similar polymer membranes
may include, for example, Flemion® (Asahi Glass), Aciplex® (Asahi
Kasei), etc., however, such polymer membranes are not commercially viable
for use in a fuel cell-based application because of their prohibitively
expensive price.

[0008] In order to reduce cost, a hydrocarbon-based electrolyte that
introduces a sulfonic acid group or phosphonic acid group to a polymer
having superior thermal stability and mechanical strength has been
developed and actively studied. For example, aromatic polyether, which is
a representative, attractively priced engineering plastic, is a polymer
in which a phenylene ring is Connected to an oxygen atom, is. The
aromatic polyester in its humidified state shows high hygroscopic
property and high hydrogen conductivity. Unfortunately, at high
temperature its performance significantly degrades due to the evaporation
of water.

[0009] As to a conventional polymer electrolyte fuel cell, one suggested
conventional art solution proposes a fuel cell consisting of an
electrolyte membrane including an ionic conductive film between a
nitrogen-containing compound, which contains histamine, and an ionic
conductive polymer. Another suggested conventional art solution proposes
a fuel cell asymmetric membrane that is a complex of polyarylene having a
sulfonic acid group and a nitrogen-containing compound (histamine).
However, the foregoing proposed solutions have the disadvantage of
extremely low mechanical strength and/or leakage of the
nitrogen-containing compounds from the polymer electrolyte membrane
during the course of long-term use of the soaked nitrogen-containing
compound.

[0010] Recently, as part of an effort to develop a polymer electrolyte
substance operable in an anhydrous/high temperature environment, the
present inventors have measured conductivities of various types of ionic
liquids soaked in the PSS-PMB polymer electrolyte. By using
alkylimidazole salt having high thermal stability, it has been found that
various nano structures are formed according to a molecular weight of a
polymer and a type and a relative content of a soaked ionic liquid.
Moreover, the conductivity of the resulting nano structures vary largely
depending upon the type of the nano structure.

[0011] By discovering such a correlation, with different molecular weights
and degrees of sulfonation of block copolymers and different types and
soaking of ionic liquids, conductivities were measured and correlations
among them were also investigated, resulting in a high conductivity of
0.045 S/cm which is the highest conductivity level known to occur at a
high temperature of 165° C. For example, such a conductivity level
is three times greater than the conductivity of Nafion®, which has a
maximum conductivity of 0.014 S/cm at 165° C. Disadvantageously,
this system experiences significant degradation of mechanical strength
because the soaked ionic liquid absorbs moisture in a humidified
environment, which causes the soaked ionic liquid to leak out of the
electrolyte membrane.

SUMMARY OF THE DISCLOSURE

[0012] The present invention provides a polymer electrolyte membrane
bonded with an ionic liquid through chemical reaction of the ionic liquid
with a novel polymer chain terminal, which provides high hydrogen ionic
conductivity and electric-chemical and thermal stability in an
anhydrous/high-temperature environment. Accordingly, the present
invention provides a polymer electrolyte membrane having superior
electro-chemical and thermal stability in an anhydrous/high-temperature
environment.

[0013] The present invention also provides a block copolymer for a
poly(styrene-block-2-histamine methylbutylene acrylate) polymer
electrolyte membrane, the poly being a novel polymer chain.

[0014] The present invention also provides a fuel cell using the polymer
electrolyte membrane.

[0015] In one aspect, the present invention provides a polymer electrolyte
membrane bonded by chemically reacting a block copolymer represented by
the Chemical Formula 1 and an ionic liquid containing a
fluorine-containing anion and an imidazolium salt cation, the ionic
liquid represented by the Chemical Formula 2,

##STR00001##

[0016] wherein x is 10-1000, and y is 10-1000, and

##STR00002##

[0017] wherein R1 and R2 are independently hydrogen and a
C1-C30 alkyl group, and X.sup.- is selected from the group
consisting of BF4.sup.-, PF6.sup.-,
C2F6NO4S.sup.-, Cl.sup.-, OH.sup.-, Br.sup.- and
CF3SO3.sup.-.

[0018] In another aspect, the present invention also provides a block
copolymer for a poly(styrene-block-histamine methylbutylene acrylate)
polymer electrolyte membrane represented by the Chemical Formula 1:

##STR00003##

[0019] wherein x is 10-1000, and y is 10-1000.

[0020] In another aspect, the present invention also provides a fuel cell
including the polymer electrolyte membrane.

[0021] Other aspects and preferred embodiments of the invention are
discussed infra.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The above and other features of the present invention will now be
described in detail with reference to an exemplary embodiment thereof
illustrated by the accompanying drawings, which are given hereinbelow by
way of illustration only, and thus are not limitative of the present
invention, and wherein:

[0023] FIG. 1 is a gel permeation chromatography (GPC) graph of a polymer
electrolyte membrane manufactured according to an exemplary embodiment of
the present invention;

[0024]FIG. 2 is an NMR spectrum graph of polystyrene-block-2-histamine
methylbutylene acrylate) manufactured according to an exemplary
embodiment of the present invention;

[0025]FIG. 3 is a small-angle X-ray scattering graph showing formation of
a nano structure after anion doping of an example synthesized polymer
electrolyte;

[0026]FIG. 4 is a small-angle X-ray scattering graph showing formation of
a nano structure of a polymer electrolyte membrane manufactured by a
comparative example according to the present invention;

[0027]FIG. 5 is a hydrogen ionic conductivity graph in an anhydrous
environment of a polymer electrolyte membrane manufactured according to
an exemplary embodiment of the present invention;

[0028]FIG. 6 is a hydrogen ionic conductivity graph in an anhydrous
environment of a an example polymer electrolyte membrane manufactured by
a comparative example according to the present invention; and

[0029]FIG. 7 is a hydrogen ionic conductivity graph measured for 320
hours at 120° C. in a polymer electrolyte membrane manufactured
according to an exemplary embodiment of the present invention.

[0030] It should be understood that the appended drawings are not
necessarily to scale, presenting a somewhat simplified representation of
various preferred features illustrative of the basic principles of the
invention. The specific design features of the present invention as
disclosed herein, including, for example, specific dimensions,
orientations, locations, and shapes will be determined in part by the
particular intended application and use environment.

DETAILED DESCRIPTION

[0031] Hereinafter, an exemplary embodiment of the present invention will
be described in detail with reference to the accompanying drawings to
allow those of ordinary skill in the art to easily carry out the present
invention. While the invention will be described in conjunction with the
exemplary embodiment, it will be understood that present description is
not intended to limit the invention to the exemplary embodiment. On the
contrary, the invention is intended to cover not only the exemplary
embodiment, hut also various alternatives, modifications, equivalents and
other embodiments, which may be included within the spirit and scope of
the invention as defined by the appended claims. Hereinbelow, the present
invention will be described in more detail with an exemplary embodiment
of the present invention.

[0032] It is understood that the term "vehicle" or "vehicular" or other
similar term as used herein is inclusive of motor vehicles in general
such as passenger automobiles including sports utility vehicles (SUV),
buses, trucks, various commercial vehicles, watercraft including a
variety of boats and ships, aircraft, and the like, and includes hybrid
vehicles, electric vehicles, plug-in hybrid electric vehicles,
hydrogen-powered vehicles and other alternative fuel vehicles (e.g.,
fuels derived from resources other than petroleum). As referred to
herein, a hybrid vehicle is a vehicle that has two or more sources of
power, for example both gasoline-powered and electric-powered vehicles.

[0033] Ranges provided herein are understood to be shorthand for all of
the values within the range. For example, a range of 1 to 50 is
understood to include any number, combination of numbers, or sub-range
from the group consisting of 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13,
14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31,
32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49,
or 50, as well as all intervening decimal values between the
aforementioned integers such as, for example, 1.1, 1.2, 1.3, 1.4, 1.5,
1.6, 1.7, 1.8, and 1.9. With respect to sub-ranges, "nested sub-ranges"
that extend from either end point of the range are specifically
contemplated. For example, a nested sub-range of an exemplary range of 1
to 50 may comprise 1 to 10, 1 to 20, 1 to 30, and 1 to 40 in one
direction, or 50 to 40, 50 to 30, 50 to 20, and 50 to 10 in the other
direction.

[0034] Unless specifically stated or obvious from context, as used herein,
the term "about" is understood as within a range of normal tolerance in
the art, for example within 2 standard deviations of the mean. "About"
can be understood as within 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%,
0.5%, 0.1%, 0.05%, or 0.01% of the stated value. Unless otherwise clear
from the context, all numerical values provided herein are modified by
the term "about."

[0037] an ionic liquid containing a fluorine-containing anion and an
imidazolium salt cation, the ionic liquid represented by the Chemical
Formula 2,

##STR00004##

[0038] wherein x is 10-1000, and y is 10-1000, and

##STR00005##

[0039] wherein R1 and R2 are independently hydrogen and a
C1-C30 alkyl group, and X.sup.- is selected from the group
consisting of BF4.sup.-, PF6.sup.-,
C2F6NO4S.sup.-, Cl.sup.-, OH.sup.-, Br.sup.- and
CF3SO3.sup.-.

[0040] According to an exemplary embodiment of the present invention, the
polymer electrolyte membrane may comprise the ionic liquid in an amount
of 30 to 50 parts by weight with respect to 100 parts by weight of the
block copolymer. If the polymer electrolyte membrane comprises the ionic
liquid in an amount of 30 parts by weight or less with respect to the
block copolymer, the ionic conductivity may be too low. On the other
hand, if the ionic liquid is present in an amount of 50 parts by weight
or more, the mechanical strength of the electrolyte membrane may be too
low.

[0041] In addition, the present invention also includes a block copolymer
for a poly(styrene-block-histamine methylbutylene acrylate) polymer
electrolyte membrane represented by the Chemical Formula 1, as a medium
of the polymer electrolyte membrane,

##STR00006##

[0042] wherein x is 10-1000, and y is 10-1000.

[0043] According to an exemplary embodiment of the present invention, the
block copolymer has excellent durability due to chemical bonding of
histamine to styrene and polyacrylic acid having high mechanical strength
(Young's modulus=2 GPa).

[0044] For the block copolymer, hydrogen peroxide (H2O2) and a
formic acid (HCOOH) may be added to poly(styrene-block-isoprene) (polymer
1) and are stirred for 7 hours at 50° C., such that
poly(styrene-block-2-hydroxy methylbutylene acrylate) (polymer 2) may be
obtained. The poly(styrene-block-2-hydroxy methylbutylene acrylate)
(polymer 2) may be stirred in an organic solvent and then histamine may
be added thereto so that a block copolymer for a
poly(styrene-block-2-histamine methylbutylene acrylate) (polymer 3)
polymer electrolyte membrane may be manufactured.

[0045] The present invention also includes a fuel cell including the
polymer electrolyte membrane.

[0046] Therefore, by manufacturing the polymer electrolyte membrane bonded
with an ionic liquid, through chemical reaction of the ionic liquid to a
novel polymer chain terminal, a high hydrogen ionic conductivity may be
achieved even in a high-temperature and anhydrous environment.
Additionally, the electro-chemical and thermal stability of the resulting
membrane is excellent. Moreover, the polymer electrolyte membrane may
also be applied to a high-temperature and dry-out bio fuel cell.

[0047] Hereinafter, the present invention will be described in more detail
based on the embodiment, without being limited by the following
embodiment.

Manufacturing Example

Synthesis of Block Copolymer

[0048] CHCl3 of 1 g/25 ml was added to polystyrene-block-isoprene)
(polymer 1) and dissolved. Thereafter, H2O2 of 1 g/2 ml and
HCOOH of 1 g/25 ml were added and stirred for 7 hours at 50° C.,
thus obtaining poly(styrene-block-2-hydroxy methylbutylene acrylate)
(polymer 2). The poly(styrene-block-2-hydroxy methylbutylene acrylate)
(polymer 2) was added to DMF/THF (1:10) and dissolved, and then cooled to
0° C., after which triethylamine (Et3N) (1.4 eq) of 1.4 ml was
added and stirred for 10 minutes. Thereafter, ethyl chloroformate (ECF)
(1.2 eq) of 0.8 ml was added to the solution and stirred for 10 minutes
at 0° C., and then continuously stirred for 30 minutes at
25° C. After the reagent was filtered, 5 ml of dimethyl formamide
(DMF), in which histamine (1.1 eq) of 0.8 g was dissolved, was added to
the filtered reagent and mixed. The reaction mixture was stirred for 30
hours, thus obtaining polystyrene-block-2-histamine methylbutylene
acrylate) block copolymer (polymer 3). The foregoing reaction mechanism
is expressed by Reaction Formula (refer to FIGS. 1 and 2):

##STR00007##

Example

Manufacturing of Polymer Electrolyte Membrane

[0049] 30 parts by weight of imidazole of the ionic liquid having various
anions (e.g., BF4.sup.-, PF6.sup.-) acting as a bronstead acid
was dissolved in THF (tetrahydrofuran, ≧99%)/MeOH and doped, after
which 70 parts by weight of poly(styrene-block-2-histamine methylbutylene
acrylate) (polymer 3) manufactured in Manufacturing Example was mixed
using the mixing solution and then stirred for 24 hours at room
temperature. After the solvent was entirely removed from the solution at
room temperature in the existence of argon (Ar), the solution was
vacuum-dried for 10 days at 50° C., thereby manufacturing a
polymer electrolyte membrane chemically bonded with the ionic liquid.

Comparative Example

Manufacturing of Polymer Electrolyte Membrane

[0050] The polymer electrolyte membrane was manufactured in the same
manner as the foregoing embodiment with the exception that the terminus
of poly(styrene-block-2-histamine methylbutylene acrylate), which is a
general polymer chain, was doped with CH3SO3--by using methane sulfonate
(hereinafter, "[MS]" for short, ≧99% HPLC grade from Sigma
Aldrich) as the ionic liquid.

Experimental Example 1

Structural Analysis of Compound Manufactured by Embodiment

[0051] The molecular weight and molecular formula of the compound obtained
in the foregoing embodiment were determined using a high-performance
liquid chromatography (HPLC) analyzer, and identification of the
structure of the compound was performed by analyzing a 1H NMR
spectrum through nuclear magnetic resonance analysis (Bruker AMX 500)
(see FIG. 2).

[0056] The SAXS experiment was conducted in a 4Cl SAX beam line of a
Pohang Light Source (PLS). For the polymer electrolyte membranes
manufactured by Embodiment and Comparative Example, small-angle X-ray
scattering data was measured in the condition of Ar and room temperature.

[0057] As shown in FIG. 3, the polymer electrolyte membranes manufactured
by Embodiment and Comparative Example have particular nano structures
with periods of 7.5 nm and 25.4 nm, respectively, at room temperature.
25.4 nm shows the periodicity of a lamella in a plate shape and 7.5 nm
indicates a size of an ionic domain formed by histamine. This means that
the histamine forms re-ordered arrangement in the polymer's nano
structure (see FIGS. 3 and 4).

[0058] The order of the lamella structure progressively increased in the
experimental series of w/o doping, BF4 doping, and PF6 doping,
respectively. Accordingly, it may be seen that hydrophobic anions are
involved in the formation of the nano structure. In other words, when the
ion is not doped, a Flory-Huggins interaction parameter inducing phase
separation of a poly(styrene-block-2-histamine methylbutylene acrylate)
polymer bonded with histamine at the polymer chain terminal thereof is
relatively small, so that a clear microphase may not be formed
(disorder); but as the anion is doped, histamine is cationized, such that
the Flory-Huggins interaction parameter increases, inducing formation of
the well-ordered lamella structure. The Flory-Huggins interaction
parameter in the disorder and lamellar structure phase boundary known in
classic block copolymer thermodynamics is 10.5, and for this reason, in
this study, the Flory-Huggins interaction parameter becomes larger than
10.5 by anion doping,

Experimental Example 3

Measurement of Hydrogen Ionic Conductivity

[0059] The hydrogen ionic conductivities of the polymer electrolyte
membranes manufactured according to Embodiment and Comparative Example
were measured using alternating-current (AC) impedance spectroscopy. A
through-plane hydrogen ionic conductivity was measured using two
electrode cells of a stainless steel blocking electrode having a size of
1.25 cm×1.25 cm and a Pt operating electrode/relative electrode
having a size of 1 cm×1 cm.

[0060] As a result, the hydrogen ionic conductivities of the polymer
electrolyte membranes manufactured according to Embodiment and
Comparative Example were obtained as 0.2 mS/cm and 3-5 mS/cm,
respectively, with different anion types, at 120° C. in an
anhydrous environment, and those values are larger than conductivity
values in an anhydrous environment, which were obtained in a system
chemically bonded with an ionic liquid. In particular, the conductivity
of the obtained hydrogen ionic corresponds well with the degree of order
of the nano structure (see FIGS. 5, 6, and 7).

[0061] The poly(styrene-block-2-histamine methylbutylene acrylate) block
copolymer manufactured as described above is thermally and chemically
stable at a high temperature of 130° C. To maximize the hydrogen
ionic conductivity of the block copolymer, BF4.sup.- having
hydrophilic property and PF6.sup.- having hydrophobic property were
doped, after which the influence upon the hydrogen ionic conductivity and
durability were evaluated, resulting in a hydrogen ionic conductivity of
0.2 mS/cm of the anion-doped polymer electrolyte membrane at an operating
temperature of 120° C. in an anhydrous environment, and a stable
hydrogen conductivity even in continuous measurement for 300 hours or
more.

[0062] On the other hand, in the case of structural analysis and
conductivity measurement of the electrolyte membrane using CH3SO3--as an
anion according to Comparative Example, as can be seen in FIG. 6, despite
the presence of the anion, the microphase was not formed at all, and the
conductivity value was not quite improved when compared to the w/o doping
case in which the ion was not soaked, resulting in a maximum conductivity
of only 0.01 mS/cm. Therefore, it can be seen that an effective way to
obtain a high hydrogen conductivity is making a path of ion conduction in
nanometer units by forming the microphase.

[0063] According to the present invention, by manufacturing a polymer
electrolyte membrane bonded with an ionic liquid through chemical
reaction of the ionic liquid to a novel polymer chain terminal, a high
hydrogen ionic conductivity may be obtained even in a high-temperature
and anhydrous environment, and the electro-chemical and thermal stability
of the resulting membrane are excellent. Moreover, the polymer
electrolyte membrane may also be applied to a high-temperature and
dry-out bio fuel cell.

[0064] While an exemplary embodiment of the present invention has been
described in detail, the protection scope of the present invention is not
limited to the foregoing embodiment and it will be appreciated by those
skilled in the art that various modifications and improvements using the
basic concept of the present invention defined in the appended claims are
also included in the protection scope of the present invention.

Patent applications by In Chul Hwang, Seoul KR

Patent applications by Nak Hyun Kwon, Seoul KR

Patent applications by Young Taek Kim, Incheon KR

Patent applications by Hyundai Motor Company

Patent applications by POSTECH ACADEMY - INDUSTRY FOUNDATION

Patent applications in class Membrane or process of preparing

Patent applications in all subclasses Membrane or process of preparing